Not applicable.
The present invention relates to a method in winding a web, in which method a roll is wound by passing the web onto a core via a pressure nip formed between a winding drum and the web roll being wound, whereby the core element is supported by means of chucks mounted on the web roll support arms.
The invention also concerns a device for winding a web, said device being designed for use in winding the web into a roll onto a core via a pressure nip formed between a winding drum and the web roll being wound, whereby the core element is supported by means of chucks mounted on the web roll support arms.
As known in the art, the web roll is supported in center-driven winders by chucks inserted in the center of the core. The chucks are mounted on the web roll support arms that are adapted laterally movable into preset positions. In some winder designs, the winding nip pressure is controlled by applying to both of the cylinders that support the web roll from its ends an equal line pressure, that is, having the cylinders connected in parallel, while in certain other designs each winder arm is controlled separately based on feedback signals obtained from sensors. A problem hampering these conventional winder constructions is that sometimes a circumferential ridge or bump will form on the web roll which causes a lateral, i.e. a side-to-side, inclination of the roll, whereby a pressure- or force-controlled feedback arrangement may result in telescoping of the roll. Obviously, this results in an unbalanced roll.
As known by those skilled in the art, this complication occurs chiefly so that the circumferential ridge gradually forming on the roll causes the roll to tilt, that is to become cone shaped, so that the pressure nip opens at one end while the other end is subjected to a high nip pressure, whereby one of the roll support arms remains higher or further from the roll axis of rotation than the other support arm when the winding operation is completed.
In regard to the prior art, reference is made to FI Pat. No. 100467, owned by the applicant, wherein a method is disclosed for use in winding a web, in which method the winding of the web takes place supported on a carrier roll onto a core via a pressure nip formed between the carrier roll and the paper roll being wound. In this prior-art method, the core rotates at least partially supported and the core/roll is supported and/or loaded by a device whose position is adjustable. During the initial stage of winding, the loading/support element(s) of the device is/are transferred by an essentially linear movement in a plane substantially passing through the axes of the carrier roll and the paper roll being wound thus accomplishing the loading and/or supporting of the roll being wound in the winding station. With the progress of the winding operation, the loading/support element(s) is/are moved downwardly along a trajectory which is substantially compliant with the perimeter of the roll being wound and, at the final stage of winding, the roll being finished is supported from below by said element(s). By virtue of said element(s), the loading and/or support force imposed on the roll being wound is controlled chiefly by the pressure nip force and the surface-drive force.
The invention is a method of controlling the position of the arms that support a web roll in engagement with a winding drum. The arms are controlled by a combination of a control unit which, based on a physics model of the winding process, predicts the roll diameter at any point in time, and force sensors mounted on the arms which detect an increase in force. The measured increase in force is used by a force feedback circuit, and the output of the feedback circuit is monitored in a feedback control unit which also receives a signal from the control unit about the predicted web roll diameter. From the feedback control unit, information is passed to parallel-operating position controllers that control the position of the roll support arms via a steering control unit which controls loading of the web roll by the hydraulic cylinders to increase the rate at which the arms move the web roll away from the winding drum, to thus prevent excessive pressure. The arms can also be controlled by electrical or mechanical means to move synchronously so as to prevent the web roll from becoming cone shaped.
It is an object of the invention to provide a method and a device capable of overcoming the complications caused by a circumferential ridge or bump which sometimes forms on a web roll as it is being wound.
It is a further object of the invention to provide a method and a device offering easier and more accurate control of the web roll structure resulting from a winding operation.
To achieve the above-stated goal and others to be described later in the text, the method according to the invention is generally characterized in that the pressing force of the nip formed between the web roll being wound according to the method and the winding drum is controlled by a position-feedback technique based on synchronized movements of the roll support arms.
Furthermore, the device according to the invention is generally characterized in that said device includes means for controlling the pressing-nip force in the nip formed between the roll and the winding drum using a position-feedback technique in which the movements of the roll support arms are synchronized.
According to the invention, the pressing-nip force is controlled using a position-feedback technique in which the movement of the roll support arms is synchronized with the help of, e.g., electrical, mechanical or hydraulic means. Mechanical synchronization can take place via, e.g., the core or the chucks, while hydraulic synchronization can be implemented using series-connected cylinders. Electrical synchronization in turn, however, has been found the most cost-efficient technique of implementing such a synchronization. According to a preferred embodiment of the invention, the implementation can be such that, e.g., one of the roll support arms is controlled by a force-feedback loop, while the other arm controlled by a position-feedback loop follows the movement of the force-controlled arm. This arrangement represents a simple electrical synchronization. Herein arises a minor risk from the possible occurrence of the circumferential ridge on the side of the position-controlled arm, whereby the structure of the wound roll may remain inferior. It is, however, possible to eliminate this risk. According to a preferred embodiment of the invention, the implementation of the electrical synchronization can be such that both arms are controlled in parallel by a position-feedback loop as a function of the roll diameter increase rate and the pressing force of the nip is taken into account as a correction term in the control loop. Advantageously, the pressing force of the nip is measured at both arms and the correction term can be formed as, for example, the sum, maximum or average value of both measurement signals. Thus, an increase of the nip force causes the center of the roll being wound to be offset from the nip at a faster rate. The results being disturbances will be effectively compensated for on either side of the roll being wound.
According to the invention, both of the roll support arms can be mechanically synchronized to each other via, e.g., the core or, alternatively, by electrical means such as a control loop in which one of the arms is controlled by a force-feedback loop and the other is synchronized to move therewith controlled by a position-feedback loop. By virtue of the control arrangement according to the invention, the structure of the roll being wound becomes easily manageable due to the above-described synchronized control of the roll support arms that allows the pressing-nip force to be controlled by a position-feedback loop.
Particularly advantageously, the invention is suited for use in conjunction with the method and apparatus disclosed in cited FI Pat. No. 100,468 owned by Metso Paper, Inc., the assignee of this application, wherein the prior-art loading/supporting arrangement can be complemented with the position-controlled center-loading technique according to the present invention for controlling the pressing-nip force.
In the following the invention will be described in greater detail with reference to the FIGURE of appended drawing to the details of which the invention is not by any means intended to be narrowly confined.